The present invention generally relates to the field of medical devices, and more particularly, to the field of catheters such as guide catheters used for the placement of medicines and medical devices within the body. Specifically, the invention is directed to a catheter tube, particularly useful in an intravascular guide catheter, incorporating a high tensile strength braid wire constraint.
The use of intravascular catheters for treatment of the body is well known in the field of medicine. The need for a choice of catheter sizes and types has grown rapidly as the techniques for their use have been greatly improved and the types of medical uses have expanded quickly. One such catheter is a guide catheter which includes a tubular member having a lumen therethrough. Guide catheters are commonly used in diagnostic and treatment techniques related to vascular disease such as angioplasty. A guide catheter is inserted into the femoral artery and routed to a location near a treatment or diagnostic site through the aorta over the aortic arch to the ostium of a target vessel. The guide catheter provides a conduit so that fluid or another medical device can be delivered easily to the proximate location of treatment via the lumen of the guide catheter.
Prior art catheters often comprise a tubular member including a pair of congruent tubes, the inner one defining the lumen. A hub is connected at the proximal end of the tubes which in addition to providing access to the lumen for fluids and the like, is often used to provide torques and other necessary pressures to the tubes during their placement within the body. A tip of a selected design is placed at the distal end of the tubes. Flexibility is an essential part of the catheter so that it may be successfully torqued, pushed and pulled on its way through the vascular passage to the desired site in the body. For control of the catheter and to prevent its kinking from excessive flexing a certain amount of rigidity is also required. The prior art catheters often meet this need for rigidity by adding a support member between the two tubes. This support member may comprise a braid of metal wire wrapped around the inner tube, and often imbedded within the outer tube.
As specific examples of the type of prior art catheters described above, note U.S. Pat. No. 3,485,234, issued Dec. 23, 1969, to R. C. Stevens, for Tubular Products and Method of Making Same; and European Patent Application, Publication No. 0 277 366/A1, Priority Jun. 1, 1987, by Bruce H. Ward, for Guiding Catheter and Method for Making it. Each of these references teaches, in general, the prior art type of catheter discussed above.
One problem that has arisen is that as it becomes desirable to increase the diameter of the catheter lumen, it also becomes desirable to decrease the thickness of the walls of the tubes that form the catheter. However, it has been found that in thinner-walled catheters it is more difficult to prevent the kinking of the catheter. This negative effect on flexibility is overcome by the above cited co-pending application, Ser. No. 08/108,973, filed Aug. 18, 1993, entitled xe2x80x9cImproved Thin-Walled Catheterxe2x80x9d which is incorporated by reference herein. The disadvantage of the prior art was overcome by providing a high tensile, stainless steel braid as the support structure. However, it has been found that the use of the high tensile metal braid may cause an additional problem for practitioners of the catheter art. It has been seen that the high tensile wire has a tendency to flare or spring out in an area proximate the ends of the braid both before and during the heating process used in joining the catheter to a tip or other apparatus. In a similar way, this flaring and springing of the support braid wire is found in prior art catheters even when using the lower tensile type of wire. This flaring will interfere in the proper joinder of the catheter to, for example, a tip and is clearly undesirable and unacceptable in an intravenous catheter.
It is recognized that guide catheters preferably have a low friction inner lumen for improved passage of other catheter devices, such as an angioplasty catheter, through such lumen. Catheters incorporating a lumen lined with polytetrafluoroethylene (PTFE) to insure low friction are generally known. The soft atraumatic tip of prior art catheters, however, does not incorporate a polytetrafluoroethylene liner. Due to the softness of the tip material and the absence of the PTFE liner, the tip area can add significant friction opposition to advancing devices through the inner lumen of the catheter. Further, it is recognized that extending the braid wire into the atraumatic tip is not desirable, as this would significantly stiffen the tip area and counter its function of providing an atraumatic positioning of the distal end of the guide catheter. Thus, it is the clinical function of the tip that requires such tip to be very soft and free of wire braid. Terminating the braid prior to the soft tip increases the prevalence of problems associated with the flaring or springing out of the wire braid proximate its free ends near the distal tip.
Accordingly, the need exists for a catheter tube construction incorporating a lubricous liner and overlying wire braid structure, wherein the free ends of the wire braid proximate the location of attachment of a soft atraumatic tip are prevented from flaring out during manufacture of the catheter tube. Further, a need exists for an atraumatic tip design which incorporates a lubricous liner to reduce the friction caused by the soft tip material when passing devices through the lumen of the tip. The present invention addresses these needs, as well as other problems associated with existing guide catheter tube and tip designs. The present invention also offers further advantages over the prior art and solves other problems associated therewith.
The present invention overcomes the above-identified disadvantages by providing an improved catheter tube incorporating a lubricous liner in combination with a wire braid overlying the lubricous liner, wherein the free ends of the wire braid are effectively restrained to overcome the inherent spring property of the material and prevent protrusion of the free ends proximal to the soft tip when assembled.
The present invention further provides a catheter tube incorporating a lubricous liner, preferably polytetrafluoroethylene, which extends at least through a portion of the inner lumen of the atraumatic tip to reduce friction therethrough. In a preferred embodiment, the liner extends through essentially the entire length of the inner lumen of the soft atraumatic tip.
The present invention further includes improved methods for joinder of the catheter to any selected apparatus, such as joinder of the tip to the catheter tube.
Two overall embodiments and methods of manufacturing these embodiments are disclosed herein. In a first embodiment, a lap-type joint is formed at the distal end of a section of catheter shaft subsequent to manufacture of a tubular member having an inner tube, an outer congruent tube and a wire braid therebetween. A means for restraining the free ends of the wire braid in the lap joint area is provided with subsequent addition of the atraumatic tip, a portion of which overlies the restrained free ends of the wire braid.
In a second embodiment, a braided shaft region and a non-braided tip region are formed over a continuous liner or inner tube, preferably a polytetrafluoroethylene liner or inner tube. This is achieved by sleeving a preformed segment of wire braid over a preformed inner tubular member or a liner. A molding sleeve is then tracked over the braid and inner tubular member which pulls the braid down tightly to the inner tubular member, including the flaring -ends of the wire braid. With the molding sleeve in place, adhesive material is applied via capillary action to the region having the molding sleeve restraining the ends of the wire braid, which when cured hold the ends in place upon removal of the molding sleeve. This design further allows the inner tubular member to extend braid-free through a tip attached proximate the end of the wire braid.
In the preferred embodiment at least one end of the catheter, normally the distal end, is ground down by an abrasion tool to provide a length of reduced diameter suitable, in particular, for lap-joint type connection to a tip or other apparatus. A restraining material, preferably a thin-walled heat shrink polyester, is also provided to be placed over at least a portion of the reduced diameter length to prevent flaring of the metal braid during the joinder process.
In this embodiment, the restraining material can be in the form of a sleeve having a tubular shape with an inner diameter adapted to allow placement of the sleeve over at least a portion of the reduced diameter length at the end of the catheter; and a length at most equal to the length of the reduced diameter portion of the catheter.
As described, the apparatus and method of this embodiment provides the advantage of allowing use of the high tensile metal braid by restraining flaring of the metal during heat bonding to a tip or other device, thus improving kink performance in the thin-walled catheters which use the high tensile wire. The embodiment provides the same restraining advantage for catheters which may not use the high tensile wire, but which have the same flaring problem. This embodiment also provides the advantage of providing a more durable bond of the catheter to the tip or other apparatus by the increased surface area of the lap type bonding. Finally, the apparatus of this embodiment offers an additional advantage in the form of a stiffness transition in that the ground or abraded step portion of the bond balances the hardness of the main catheter to the softness of a tip, a balance which is known to provide clinical value.
In the second embodiment of the present invention, a catheter shaft construction is provided that incorporates adhesive means for preventing the free ends of a braid member from flaring outward during assembly. Further, this embodiment also provides a continuous inner tubular member or liner that is preferably lubricous, such as polytetrafluoroethylene, which extends through the tip portion of the catheter tubular member, yet has a portion which is free of the braid member. With the inner liner extending through the catheter shaft and tip, the braid or braid wire ends uniformly just proximal to the beginning of the distal soft tip, which results in the above-identified flaring of the braid wire. Thus, a preferred method has been developed to restrain the flaring braid wires during assembly of the catheter shaft which provides for a continuous liner for both the shaft and tip regions and a braid-free tip section. The method does not require braid removal and does not add wall thickness to restrain the flared ends.
With this second preferred embodiment, a first step in the method of manufacture is to form a braided shaft region and a non-braided tip region over a continuous liner. This is preferably achieved by sleeving the braid or wire braid over a section of liner which is placed over a core or mandrel. The distal end of the braid terminates proximal to the distal end of the liner to separate the shaft and tip regions.
A molding sleeve is then tracked over the braid and liner. The molding sleeve is preferably a tubular member having a lumen therethrough which, when tracked over the braid, pulls the braid wire down tightly to conform to the outer longitudinal surface of the liner. At the end of the wire braid, the advancing molding sleeve forces the free braid ends to conform back into the original braid pattern and into the lumen of the molding sleeve. Once the distal ends of the braid member have been conformed by the molding sleeve, adhesive means is injected into the cavity between the molding sleeve and the liner over a portion of the braid proximate its distal end. Preferably a high temperature (350-400xc2x0 F.), soft (25D-50D) restraining seal in liquid form is injected into the cavity. Capillary action is recognized as facilitating this process by sucking the liquid seal restraining material from outside the molding sleeve to inside.
The liquid seal is then cured through the molding sleeve. A preferred adhesive means is an ultraviolet light (UV) curable adhesive which is used in conjunction with a clear molding sleeve that allows UV light to pass through the clear molding sleeve walls which cures the adhesive. Although other adhesives and curing methods and appropriate adhesives are recognized as within the scope of the invention, including such methods as heat, catalyst and moisture.
Upon removing the molding sleeve, the resulting intermediate assembly or tubular assembly includes a micro-thin band molded from the adhesive means or liquid seal that circumferentially encapsulates the distal free wire ends. The restraining band preferably adheres to the liner and encapsulates the wire braid. The band is very thin, uniform in thickness, and concentric, due to the forming of the liquid seal within the molding sleeve. The wire braid ends are uniformly and distinctly ended while the inner tubular member or liner continues distally to provide a braid-free region for tip attachment.
An outer tubular member overlies the intermediate tube assembly over at least a portion of the assembly having the braid thereon. A tip member overlies the portion of the liner which extends distally beyond the braid. The distal end of the tip member can extend beyond the distal end of the liner, but in preferred embodiments, the tip-member is co-extensive with the liner to provide an atraumatic tip having a continuous liner therethrough.
These and other various advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and the objects obtained by its use, reference should be made to the drawings which form a further part hereof and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the present invention.
The present invention overcomes the disadvantages found in the prior art by providing an improved metallic support member that has a greater tensile strength and a greater Modulus of Elasticity than non-metallic support materials and therefore can offer an increase in the rigidity required to prevent kinking without sacrificing the needed flexibility. The increased tensile strength of the present invention is primarily achieved through the tempering or hardening of the metal used for the support member. In the prior art, the support member, such as a stainless steel braid, was annealed, thus resulting in a comparatively low tensile strength.
In the preferred embodiment of this invention the support member comprises a braid made of tempered stainless steel wires. A fully hardened metal wire is preferred, such as #304 stainless steel which will yield a tensile strength in the range of 300 to 475 kilopounds per square inch (kpsi) and which has a Modulus of elasticity ranging from 28,000,000 psi fully hardened to 26,000,000 not fully hardened. Other types of stainless steel can be used, including those having lower tensile strength. It has been found that tensile strengths as low as 200 kpsi offer advantageous kink performance.
Also, in the preferred embodiment of this invention, the preferred diameter of the braiding wire has been found to be 0.002 inches. However, it should also be noted that other diameters can be successfully utilized, such as in the range of 0.00075 to 0.0035 inches, dependent on the dimensions of the catheter thin wall.
In the preferred embodiment of this invention it has further been found that the preferred braid construction is 16 strands of tubular braid, with a braid density of 40 crosses per inch (pic). Other combinations of braid strands and pic densities have also been found to be useful.